DESCRIPTION (Applicant's abstract): The proposed project is designed to investigate the nature of reasoning impairments in dementia of Alzheimer's type, and related disorders. In addition, by integrating neuropsychological data with brain imaging data, the study seeks to determine the roles of different brain regions in reasoning. The performance of three groups of patients will be compared on tests of working memory, declarative memory, and reasoning: 1) a group of patients with focal damage to prefrontal cortex, 2) patients with damage limited to anterior regions of temporal cortex, and 3) patients with damage to posterior cortical areas, producing dementia of Alzheimer's type. A group of age-matched control subjects will also be tested. Items from reasoning tests systematically vary in the number of relational representations they require reasoners to simultaneously manipulate. It is proposed that intact prefrontal cortex is essential for successful reasoning because it is required for the integration of relations between objects and events. Thus, it is hypothesized that patients with damage to prefrontal cortex will show significant impairment, relative to patients with Alzheimer's disease, on items which require relational integration. Additionally, it is predicted that a double dissociation will be found between relational reasoning and declarative memory abilities in patients with damage to prefrontal cortex and patients with Alzheimer's Disease. Finally, I hypothesize that significant correlations will be observed between scores on measures of working memory and relational reasoning in all participant groups.